Spitzer made the announcement without having finalized a plea deal with federal prosecutors, though a law enforcement source familiar with the investigation said he is believed to still be negotiating one. The official spoke on condition of anonymity because of the sensitivity of the case.

"Over the course of my public life, I've insisted, I think correctly, that people regardless of their position or power take responsibility for their conduct. I can and will ask no less of myself," Spitzer said at a Manhattan news conference with his wife, Silda, at his side. He left without answering questions.

Spitzer will be replaced on Monday by Lt. Gov. David Paterson, who becomes New York's first black governor. He also will be the state's first legally blind governor and its first disabled governor since Franklin D. Roosevelt.

Paterson issued a statement in which he said he was saddened, but would move forward. "It is now time for Albany to get back to work as the people of this state expect from us," he said.

The scandal erupted Monday when allegations surfaced that the 48-year-old father of three daughters spent thousands of dollars on a call girl at a swanky Washington hotel on the night before Valentine's Day.

Spitzer was more composed than he was earlier in the week, when he apologized for an undisclosed personal failing and looked pale, drawn and glassy-eyed. His wife took deep breaths as each of Spitzer's words was accompanied by a rush of camera clicks.

"I look at my time as governor with a sense of what might have been," Spitzer said.

Attending the news conference with Spitzer were his close advisers and lawyers, including Ted Wells, a prominent attorney who recently represented I. Lewis "Scooter" Libby.

The resignation came after two days of furious activity. Calls for his resignation came immediately after news of the allegations broke. Republicans began talking impeachment if he didn't step aside.

The case started when banks noticed frequent cash transfers from several accounts and filed suspicious activity reports with the Internal Revenue Service, a law enforcement official told The Associated Press. The accounts were traced back to Spitzer, leading public corruption investigators to open an inquiry.

Law enforcement officials said he was the person identified as "Client 9" in court papers who paid thousands for a night in a Washington hotel with a prostitute named Kristen. According to an affidavit, a federal judge approved wiretaps on the phones of the escort service in January and February.

FBI agents in Washington put Spitzer under surveillance at least twice  on Jan. 26 and Feb. 13  to confirm that a prostitute joined him at the Mayflower Hotel, according to a senior law enforcement official with knowledge of the case. The official spoke on condition of anonymity because of the sensitivity of the investigation.

The stakeouts came after the FBI recorded phone calls by Spitzer arranging the tryst, the official said.

The wiretaps were necessary as part of the investigation into whether Spitzer violated the Mann Act, which makes transportation of someone across a state line for prostitution a federal crime, the official said. Authorities in Washington now are weighing whether to prosecute Spitzer for soliciting and paying for sex  a felony in the District of Columbia, the official said.

Whether U.S. Attorney Jeffrey Taylor, who prosecutes federal and local laws in the District of Columbia, will bring charges against Spitzer likely depends on the plea deal the governor is negotiating with the government in New York, two senior law enforcement officials said.

In a statement issued after Spitzer's resignation, U.S. Attorney Michael Garcia said there was no deal with the fallen governor: "There is no agreement between this office and Governor Eliot Spitzer, relating to his resignation or any other matter."

Spitzer, a first-term Democrat, built his political reputation on rooting out government corruption, and made a name for himself as attorney general as crusader against shady practices and overly generous compensation. He also cracked down on prostitution.

He was known as the "Sheriff of Wall Street." Time magazine named him "Crusader of the Year," and the tabloids proclaimed him "Eliot Ness." The square-jawed graduate of Princeton University and Harvard Law was sometimes mentioned as a potential candidate for president.

He rode into the governor's office with a historic margin of victory on Jan. 1, 2007, vowing to stamp out corruption in New York government in the same way that he took on Wall Street executives with a vengeance while state attorney general.

His term as governor has been fraught with problems, including an unpopular plan to grant driver's licenses to illegal immigrants and a plot by his aides to smear his main Republican nemesis. The prostitution scandal, some said, was too much to overcome.

Barely known outside of his Harlem political base, Paterson, 53, has been in New York government since his election to the state Senate in 1985. He led the Democratic caucus in the Senate before running with Spitzer as his No. 2.

Though legally blind, Paterson has enough sight in his right eye to walk unaided, recognize people at conversational distance and even read if text is placed close to his face. While Spitzer is renowned for his abrasive style, Paterson has built a reputation as a conciliator.

At a morning news conference, Senate Majority Leader Joseph Bruno, Spitzer's chief rival, said he was moving on with the business of the state. Lawmakers were set to vote on budget bills Wednesday afternoon.

"We are going to partner with the lieutenant governor when he becomes governor," said Bruno. "David has always been very open with me, very forthright ... I look forward to a positive, productive relationship."

Bruno, though the next highest-ranking official, does not become lieutenant governor upon Paterson's ascension to governor. The lieutenant governor's office would remain vacant until the next general election in 2010 under state law. However, whenever Paterson is out of state or if he were to become incapacitated, Bruno would be acting governor.